These studies are generally concerned with the involvement of intercostal muscle afferents (i.e., from muscle spindles and tendon organs) in the central control of respiration. Two reflexes arising from middle and caudal intercostal muscles will be of particular interest. These reflexes are known to have spinal effects on other respiratory muscles, but their interaction with the medullary-pontine centers is not known. The first and second objectives are to determine if the "intercostal-to-phrenic" reflex, arising from mid-thoracic (T5-T8) external intercostal muscles, involves respiratory neurons located near the nucleus of the tractus solitarius (NTS) and those in the nucleus retroambigualis (NRA). The third objective is to determine if the "intercostal-to-phrenic" reflex, arising from caudal-thoracic (T9-T13) external and internal intercostal muscles has a supra-spinal arc, and if it involves both of the medullary respiratory neuron groups (NTS and NRA). The fourth objective tests the question of whether internal intercostal muscle afferents from the mid-thoracic region ascend to and affect the medullary respiratory neurons (NTS and NRA). The above objectives will be approached by monitoring the effects on medullary respiratory neuron activity of electrically stimulating the afferent nerve fibers responsible for the reflexes. The fifth objective is to investigate the involvement of these two "intercostal-to-phrenic" reflexes in the respiratory response to prolonged compression of the rib-cage. The respiratory response to chest compression will be observed before and after deafferenting (thoracic dorsal rhizoomies) the mid-thoracic (T5-T8) and caudal-thoracic (T9-T13) regions.